[time-nuts] LT1763

Bob Camp lists at cq.nu
Mon Oct 5 20:41:35 UTC 2009


The only thing I'd add to that is to be very careful of where the return on
the EFC voltage goes. 

A "ground drop" in common between the EFC and heater current can really mess
things up. A milivolt is pretty easy to come up with as the oven compensates
for significant temperature change. That same milivolt getting into the EFC
can also give you a very measurable frequency change.


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Poul-Henning Kamp
Sent: Monday, October 05, 2009 4:20 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] LT1763

In message <abec162c0910051310x11997102o2b6521fee56f1303 at mail.gmail.com>,
Green writes:

>Thanks Poul,I had not considered that one probably because of the package.
>It does look like a contender. I am considering the LT3080 because of the
>tight regulation and it is available in not one, but 2 power packages.  The
>tab is tied to the output though. The max current is around 300 mA cold and
>less than 100 mA warm. The oscillator seems to have a regulator inside
>already but does move around with voltage changes

You should pick your poison carefully here:

Low noise regulators are usually not very stable, typically they
are quite sensitive to temperature.

Precision regulators are stable, but tend to be noisy.

If your OCXO is voltage sensitive, make sure to connect the sense
resistor to the terminal, right at the OCXO VCC terminal.

If the heater has a separate VCC terminal on the OCXO, give it its
own supply.

Another trick: if you don't plan to run your OCXO in high temperatures
is to insulate it thermally.

That will reduce the current draw from the heaters, making regulation
easier, and if done right, will also low-pass-filter the temperature

But don't overdo it, it has to be able to get rid of excess heat
and you may shorten the electronics life if it gets too hot.


Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.

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